R&ocirc;le de la chalcone synthase dans la biosynth&egrave;se des flavono&iuml;des au cours de la croissance annuelle des pousses de noyers hybrides (<em>Juglans nigra &times; Juglans regia)</em> adultes et rajeunis. Applications &agrave; l&#39;enracineme

Au cours de la croissance des pousses annuelles de noyer hybride (Juglans nigra &times; Juglans regia), le rajeunissement est marqu&eacute; par une augmentation de la teneur en hydrojuglone glucoside (naphtoquinone) en d&eacute;but de croissance et une diminution de celle en myricitrine (flavonol) en fin de croissance. Ces modifications sont particuli&egrave;rement nettes dans la moelle l&#39;ann&eacute;e du rec&eacute;page, dans le phlo&egrave;me et &agrave; un degr&eacute; moindre dans l&#39;&eacute;corce l&#39;ann&eacute;e suivante. La pr&eacute;paration de la chalcone synthase du noyer (premi&egrave;re enzyme de la voie de biosynth&egrave;se des flavono&iuml;des) a n&eacute;cessit&eacute; l&#39;utilisation d&#39;acide ascorbique &agrave; forte concentration afin d&#39;obtenir &agrave; pH 6,8 une r&eacute;action compl&egrave;te, stable et reproductible. Par ailleurs, nous avons pu montrer l&#39;inhibition de la chalcone synthase par la c&eacute;rul&eacute;nine et les produits de la r&eacute;action et la non-inhibition par les flavonols. Une relation entre l&#39;activit&eacute; chalcone synthase et l&#39;accumulation des principaux flavono&iuml;des du noyer a &eacute;t&eacute; mise en &eacute;vidence au niveau de la pousse enti&egrave;re et plus pr&eacute;cis&eacute;ment de l&#39;ensemble des tissus &laquo;&eacute;corce et phlo&egrave;me&raquo;. L&#39;activit&eacute; chalcone synthase des pousses de noyer cultiv&eacute;es in vitro a &eacute;t&eacute; modul&eacute;e par des apports exog&egrave;nes et par l&#39;expression du g&egrave;ne chalcone synthase antisens. En culture in vitro, nous avons ainsi pu montrer une relation entre un relentissement du m&eacute;tabolisme des flavono&iuml;des et une augmentation de l&#39;aptitude &agrave; l&#39;enracinement. Les r&eacute;sultats obtenus &agrave; partir de pousses transform&eacute;es par le g&egrave;ne chalcone synthase antisens nous conduisent &agrave; &eacute;tudier la r&eacute;gulation de l&#39;expression du g&egrave;ne chalcone synthase antisens en particulier au niveau du phlo&egrave;m

Chalcone synthase activity and polyphenolic compounds of shoot tissues from adult and rejuvenated walnut trees.

Changes in the metabolism of naphthoquinone and flavonoids during the growth of half-sib adult and rejuvenated walnut shoots (Juglans nigra&thinsp;&times;&thinsp;Juglans regia L.) were studied at the tissue level for two years after pruning. Moreover, the role of chalcone synthase (CHS; EC 2.3.1.74) in the regulation of flavonoid biosynthesis was investigated at the level of enzyme activity. The end products of walnut flavonoid biosynthesis, myricitrin and quercitrin, which accumulated in the bark and phloem at the end of growth, did not inhibit the biosynthetic process at concentrations of up to 100&thinsp;&mu;M each. There was no evidence of CHS regulation by feedback or similar mechanisms which might modulate enzyme activity. Mathematical correlation of CHS activity and flavonoid accumulation during shoot growth, however, indicated that CHS is the rate-limiting enzyme of the pathway in bark and phloem and that flavonoids seem to be transported from phloem to bark where they accumulated mainly during growth. In defoliated shoots, naphthoquinone metabolism appeared to be a marker of the walnut rejuvenation stage in the medulla, phloem and buds immediately after cutting and thereafter mainly in buds one year after cutting. Chalcone synthase and flavonoid contents appeared to be markers of the adult stage in the phloem

Expression of chalcone synthase gene in walnut.

A rapid and efficient method has been succesfully applied to the isolation and purification of RNA from lyophilised tissues of walnut trees (Juglans sp.) particularly rich in phenolic compounds and polysaccharides. The quality of the extracted RNA has been characterized by gel electrophoresis and Northern blot hybridization

Modalités de décision de limitation thérapeutique chez les traumatisés crâniens sévères : enquête auprès des neurochirurgiens en France

International audienc

Molecular cloning and functional expression of a stress-induced multifunctional <em>O</em>-methyltransferase with pinosylvin methyltransferase activity from Scots pine (<em>Pinus sylvestris</em> L.).

Formation of pinosylvin (PS) and pinosylvin 3-O-monomethyl ether (PSM), as well as the activities of stilbene synthase (STS) and S-adenosyl-1-methionine (SAM):pinosylvin O-methyltransferase (PMT), were induced strongly in needles of Scots pine seedlings upon ozone treatment, as well as in cell suspension cultures of Scots pine upon fungal elicitation. A SAM-dependent PMT protein was purified and partially characterised. A cDNA encoding PMT was isolated from an ozone-induced Scots pine cDNA library. Southern blot analysis of the genomic DNA suggested the presence of a gene family. The deduced protein sequence showed the typical highly conserved regions of O-methyltransferases (OMTs), and average identities of 20-56% to known OMTs. PMT expressed in Escherichia coli corresponded to that of purified PMT (40 kDa) from pine cell cultures. The recombinant enzyme catalysed the methylation of PS, caffeic acid, caffeoyl-CoA and quercetin. Several other substances, such as astringenin, resveratrol, 5-OH-ferulic acid, catechol and luteolin, were also methylated. Recombinant PMT thus had a relatively broad substrate specificity. Treatment of 7-year old Scots pine trees with ozone markedly increased the PMT mRNA level. Our results show that PMT represents a new SAM-dependent OMT for the methylation of stress-induced pinosylvin in Scots pine needles

Induced Responses in Phenolic Metabolism in Two Norway Spruce Clones after Wounding and Inoculations with Ophiostoma polonicum, a Bark Beetle-Associated Fungus.

Two Norway spruce (Picea abies Karst.) clones, one resistant and the other susceptible to mass inoculation with Ophiostoma polonicum Siem., were compared with regard to their phenolic compositions and chalcone synthase (CHS) and stilbene synthase activities of their phloem before and at 6 and 12 d after artificial inoculation with sterile malt agar or O. polonicum. In unwounded phloem, the resistant clone differed from the susceptible clone by the presence of taxifolin glycoside, lower concentrations of stilbene glycosides, and higher CHS activity. After inoculation, (+)-catechin concentration and CHS activity dramatically increased around the wound, particularly in the resistant clone. Stilbene synthase activity also increased, but more slowly and to a lower level, whereas the concentrations of stilbenes remained stable. Tanning ability decreased in the susceptible clone, whereas it remained stable in the resistant one. It is proposed that the induced phenolic response of Norway spruce phloem consists of an activation of the phenolic pathway, finally leading to tannins and insoluble polymers. It is suggested that resistance to O. polonicum depends on the ability of the tree to easily activate the flavonoid pathway